<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
<style type="text/css">
	.mf {font-size: 40px;}
</style>
<script type="text/javascript">
	function load() {
		var txt = document.getElementById("first");
		
		//通过javascript改变元素的css类
		txt.className = "mf";
		
		//通过javascript修改css属性
		txt.style.color = "red";
	}
</script>
</head>
<body onload="load();">
	<span id="first">这是中国</span>	
</body>
</html>